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17.4 % of K2SO4 at 27°C isotonic with 4% NaOH at the same temperature. If NaOH is 100% ionised than,what is the degree of dissociation of K2SO4. ??

 

Helppp plzzz!!!!

Posted by Yash Sahu (Jul 23, 2017 9:07 a.m.) (Question ID: 6860)

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17.4 % of K2SO4 at 27°C is isotonic with 4% NaOH at the same temperature. If NaOH is 100% ionised than what is the degree of dissociation of K2SO4

Posted by Yash Sahu (Jul 22, 2017 7:30 p.m.) (Question ID: 6837)

  • Comeonn someone plz help me...

    This is really very important!!!!

    Posted by Yash Sahu (Jul 22, 2017 8:05 p.m.)
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Give the mechanisum of the reaction between propene and HBr in the presence of preoxide

 

Posted by Jemini Maheshwari (Jul 22, 2017 11:19 a.m.) (Question ID: 6827)

  • This rxn.is also called anti markovnikov's law.

    Posted by Yash Sahu (Jul 22, 2017 8:20 p.m.)
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  • Mechanism:-- As in the presence of any peroxide ,the negative part of the alkyl halide( here-Br) always gets attached to that carbon atom of alkene which has more no.of H atom therefore,

    CH3CH=CH+ HBr (In peroxide) 

    ----------> CH3CH2CH2Br 

     

     

    Answered by Yash Sahu (Jul 22, 2017 8:19 p.m.)
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adsorbtion

Posted by Saurav Yadav (Jul 19, 2017 10:20 p.m.) (Question ID: 6778)

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  • Adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface. This process creates a film of the adsorbate on the surface of the adsorbent.

    Answered by Ashutosh Kumar (Jul 20, 2017 10:09 a.m.)
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What are differences between vitamin and halogen ?

 

Posted by Ekta Sangwan (Jul 19, 2017 6:04 p.m.) (Question ID: 6764)

  • The question seems to be erroneous as  there can not  be any comparision between  vitamins  and  halogen.

    Actually the question should be ,

    " What aredifferences between vitamins  and  halogen containing  drugs (organic compounds )" ?

    Posted by Dr. Kamlapati Bhatt (Jul 20, 2017 10:23 p.m.)
  • The question seems to be erroneous  , as  the terms ' vitamin ' and ' halogen  '   are  widely  different  and hence, not  comparable.

    Actually ,   the question should be,

    " What is the difference between  vitamin  and  halogen containing drugs ( organic  compounds ) " ?   

    Posted by Dr. Kamlapati Bhatt (Jul 20, 2017 9:34 p.m.)
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  • Following  are the points  of  differences  between  vitamins   and  halogen containing  drugs ,

       

    Vitamins are certain organic compounds required in small amounts in our diet but thier defficiency causes deseases.                             Most of the vitamins cannot be synthesised in our body but plants  can synthesise all of them.

    Different vitamins belong to various chemical classes  and it is difficult to classify them on the basis of their structures.

    These have been classified  as  (i) fat soluble vitamins  viz. vitamins A,D,  Eand K

    (ii) Water soluble vitamins , viz. B group vitamins and vitamin C 

    They perfom  specific biological functions for normal maintenance of optimal growth  and health of organism.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            

                                                           Halogen containing drugs
                                                                                          These are clinically useful. 
       

                                                                  A few examples are :

                                                             Chlorine containing  antibiotic ,                                                                    chloramphenicol is very effective for                                                             treatment of  typhoid                                                                                      fever,chloroquine is used for                                                                       treatment of malaria,Halothane is                                                                  used for as an anaesthetic during                                                               surgery.a hormone thyroxine  is                                                                    produced by iodine in our body .

     

    Answered by Dr. Kamlapati Bhatt (Jul 20, 2017 10:18 p.m.)
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Slow reactions requires low activation energy as compared to fast reactions. Do you agree with this statement? 

Posted by Mamta Vaish (Jul 19, 2017 12:47 a.m.) (Question ID: 6752)

  • No

    Posted by Nitin Mhamane (Jul 19, 2017 10:37 a.m.)
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  • No because the threshold energy remains the same irrespective of it's speed. Hence speed do not depends upon the activation energy 

    Answered by Durgesh Bishi (Jul 19, 2017 2:53 p.m.)
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  • No because the threshold energy remains the same irrespective of it's speed.. Hence speed do not depends upon the activation energy 

    Answered by Durgesh Bishi (Jul 19, 2017 2:53 p.m.)
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What is the value of rate constant K at extremely high temperature (T =infinity). Is this rate constant possible? 

Posted by Mamta Vaish (Jul 19, 2017 12:46 a.m.) (Question ID: 6751)

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  • Rate constant k=AeEa/RT

    AS temperature is infinite, K=A.

    Answered by Durgesh Bishi (Jul 19, 2017 2:56 p.m.)
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  • At 338K the value i <font size="+1">2.40 x 10-3</font>

    Answered by Dr Pathikrt Banerjee (Jul 19, 2017 1:03 p.m.)
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Can a reaction have negative activation energy? 

Posted by Mamta Vaish (Jul 19, 2017 12:44 a.m.) (Question ID: 6750)

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  • Yes sometime it is negative in case of backward reaction 

    Answered by Durgesh Bishi (Jul 19, 2017 2:57 p.m.)
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  • Reaction never have negative activation energy.Its always a positive quantity.

    Answered by Nitin Mhamane (Jul 19, 2017 10:38 a.m.)
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What effect does doubling the initial concentration of a reaction on the half life of a zero order reaction. 

Posted by Mamta Vaish (Jul 18, 2017 10:02 p.m.) (Question ID: 6744)

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  • There is no effect of altering the concentrations of reactant on zero order reaction,since they are concentration independent.

    Answered by Nitin Mhamane (Jul 19, 2017 10:40 a.m.)
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Can a reaction have negative activation energy. 

Posted by Mamta Vaish (Jul 18, 2017 10 p.m.) (Question ID: 6743)

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  • Never

    Answered by Nitin Mhamane (Jul 19, 2017 11 a.m.)
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Why hydrogen and oxygen do not react at room temperature. 

Posted by Mamta Vaish (Jul 18, 2017 9:25 p.m.) (Question ID: 6742)

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  • This is because  the speed of the molecules in the gaseous mixture  at room temperature does not provide enough kinetic energy  to activate the reaction during  collision between the reactants . A mixture of  gases is formed with potential to  react or explode violently  , if sufficient energy is given. to such a gaseous mixture .Even introduction of an spark to this mixture results in raised temperature among some of the hydrogen and oxygen molecules causing  their faster collision .  This , then results into an exothermic reaction proceeding violently .

    2H2(g)   +   O2(g)   --------->    2 H2 O (g)         

    Answered by Dr. Kamlapati Bhatt (Jul 19, 2017 12:07 p.m.)
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  • The activation energy barrier to the reaction is indeed very large. The Arrhenius equation allows the rate constant, k, for a reaction to be determined: 

    k = Ae^(-Ea/RT) 

    where A = Arrhenius pre-exponential factor (depends on the system in question) 
    Ea = activation energy barrier in J/mol 
    R = 8.314 J/(K·mol) 
    T = absolute temperature in K 

    If Ea is sufficient large, k can be so close to zero that the reaction essentially will not occur at the temperature

    Answered by Ashutosh Kumar (Jul 19, 2017 11:52 a.m.)
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WHY DO ABSOLUTE VALUE OF ELECTRODE POTENTIAL  CAN NOT BE DETRMINED?

Posted by Abhishek Raj (Jul 17, 2017 9:14 a.m.) (Question ID: 6704)

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  • It is because  practically we fail to determine electrode  potential of a half cell consisting of an electrode dipped in its own salt solution. We, can measure only the difference between two half - cell potentials. that gives emf of the cell . If we arbitrarily choose the potential of one of the electrode ( half cell ) then  that of the other can be determined  with respect to this.  Therefore  ,   we need to set up a galvanic cell  consisting of two half cells , and measuring  out its  EMF.  This is possible only when we construct a cell with two half cells  & calculate its  EMF  (  in volts ) using the expression

    Eo cell  =  EoR  -  EoL 

    Hence ,   electrode potential  of  one of the half cells  must be  known .  As per IUPAC norms  Hydrogen electrode  has been chosen  under standard conditions (ie. H  with  1 bar  press . ,[ H+ ]  =  1 M  &   at 298 K  )  with its arbitrarily fixed electrode potential as   equal to zero.

    So , the reduction electrode potentials of all the different electrodes have been determined  and reported as electrode potential  relative to that of  hydrogen electrode .  

     

     

     

      

    Answered by Dr. Kamlapati Bhatt (Jul 18, 2017 9:51 p.m.)
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Define electrode. Also define half cell.

Posted by Pratik Banerjee (Jul 16, 2017 9:56 a.m.) (Question ID: 6675)

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  • An electrode is an electrical conductor that makes contact with the nonmetallic circuit parts of a circuit, such as an electrolyte, semiconductor or vacuum.

    A half cell is one of the two electrodes in a galvanic cell or simple battery. For example, in the Zn-Cu battery, the two half cells make an oxidizing-reducing couple. Placing a piece of reactant in an electrolyte solution makes a half cell.

    Answered by Payal Singh (Jul 20, 2017 6:51 p.m.)
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How ccp structure have 4 spheres

Posted by Azhar Khan (Jul 09, 2017 9:01 p.m.) (Question ID: 6520)

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  • Face centred  cubic  (fcc)   or   Cubic closed pack (ccp) -  these are the two names for the same lattice.

    We can thhink of this cell as being made by another atom into each face of a simple cubic lattice -  hence the " face centred cubic "  name .

    In such a unit cell there are atoms at all the corners , and at the centre of all the faces of the cube.

    Each atom located at the face - centre is shared between two adjacent cells and only half of the atom belongs to a unit cell. Thus ,the number of atoms  in this cell  are ,

    (i)    8 corner atoms  x  {tex}\frac{1}{8}{/tex} atom per unit cell   =   8  x  {tex}\frac{1}{8}{/tex} =  1 atom

    (ii)   6 atoms  at the faces x{tex}\frac{1}{2}{/tex} atom per unit cell =  6 x {tex}\frac{1}{2}{/tex} =  3 atoms

    {tex}\therefore{/tex} Total number of atoms per unit cell                               =   4  atoms

     

    Answered by Dr. Kamlapati Bhatt (Jul 21, 2017 2:40 p.m.)
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Why nitrogen is a gas and phosphorus is a solid

 

Posted by Jagdish Rathore (Jul 09, 2017 6:13 p.m.) (Question ID: 6515)

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  • N​​​​​​2 is exist as diatomic molecule in which two nitrogen atoms are attached to each other by triple bond this triple bond is due to p(π)-p(π) multiple bonding (sidewise overlapping) and such bonding is not possible in phosphorus due to it's large size but possible in nitrogen due to it's small size.

    In case of phosphorus four atoms are associated so it have high molecular mass, large magnitude of venderwall forces so phosphorus is solid and nitrogen is gas.

    Answered by Payal Singh (Jul 09, 2017 6:57 p.m.)
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Sign of cathode and anode for electrolytic cell. 

Posted by Pratik Banerjee (Jul 08, 2017 10:51 p.m.) (Question ID: 6490)

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  • Cathode (-ve) and Anode (+ve) sign for electrolytic cell.

    Answered by Aman Kumar (Jul 08, 2017 11:08 p.m.)
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Aplication of khlrusch law

Posted by Sneha Sharma (Jul 02, 2017 12:12 p.m.) (Question ID: 6309)

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  • Calculating molar conductivity at infinite dilution for weak electrolytes

    Degree of dissociation ¢cm÷¢minfinity(¢=lambda)

    Dissociation constant kc=c(alpha)2÷1-(alpha)

    Solubility of soluble NaCl

    Answered by Ajay Karthikeya (Jul 02, 2017 2:03 p.m.)
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How are the results of revaluation and compartment papers are given and plz tell how to score well in chemistry compartment exam 

Posted by Karthik Agarwal (Jul 01, 2017 2:11 p.m.) (Question ID: 6289)

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  • Answers to all queries related to CBSE 12th compartment result 2017 are are authentically  available at  cbse.12thresultsnic.in/compartment-result.html  However ,looking to your incusitiveness the following  is reproduceed -

    • The CBSE 12th Supply Exam Results willl be available on official website in third week of August Month ,( may be 20th of the month ). All candidates are eligible to see their results through @ cbseresullts.nic.i
    • How to check CBSE Supply Results 2017
    1. . log on to official website cbseresults.nic.in
    2.  Click link CBSE XII Compartment Results 2017
    3.  Enter your Re Exam roll no.
    4. .  Click to enter
    5. Your 12th Compartment Result Mark sheet on Screen
    6. Download and save
    7. Take a printout

     Central Board of Secondary Education has successfully  conducted 12th Supplementary Exam in July .Hence it is supposed that you must have 

    appeared , and done well .   Pl. keep awaiting for results , till Aug .2017. Now , no points in providing you tricks / methodology to score maximum in Chemistry paper..     

    Feel free to discuss with us regarding your career  /  courses   etc.

    Wish you all the best.

     

    Answered by Dr. Kamlapati Bhatt (Jul 03, 2017 5:08 p.m.)
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Write the reaction of ethanal which iilustrates the acidic propert of a-hydrogen.

Posted by Zehra Khadeeja (Jun 30, 2017 2:30 p.m.) (Question ID: 6272)

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  • A typing error !  Pl. read   as , 

    .......................................CH3 ** C* H  O   , instead  of  H** C* HO

      Thanks,

     

    Answered by Dr. Kamlapati Bhatt (Jul 01, 2017 1:42 p.m.)
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  •  

     

     

    Aldehydes and ketones exhibit the  unusual acidity of hydrogen atoms attached to Carbons - alpha  (   {tex}\alpha{/tex}  )  which is  adjacent  to that of  the carbonyl group. These hydrogens are referred as  {tex}\alpha{/tex} - hydrogens , and the carbon atom to which they  are bonded is {tex}\alpha{/tex}- carbon. In ethanal there is one {tex}\alpha{/tex}  C* & three {tex}\alpha{/tex}. - H  atoms ( marked as H** ).

    ................................H3 **  .C*  H O

    although weakly acidic ,  ( Ka  =  10-19  to 10-20 )  {tex}\alpha{/tex} - H can react  with strong bases to form anion . The unnusual acidity of {tex}\alpha{/tex} - H can be explained by both electron withdrawing ability of the carbonyl ( =CO ) group ,and resonance in anion that is formed . The electron withdrawing ability  of   =CO group is  caused by the groups di[pole nature which results by difference in electronegativities  of   C  and  O atoms.

    The anion formed by loss of {tex}\alpha{/tex} - hydrogen can be resonance stabilised because of mobility of {tex}\pi{/tex} - electrons that are adjacent to carbonyl group ( =CO ) . This resonance which stabilises the anion ( commonly termed as  enolate ion ) creates two resonance structures  , an enol & a keto-form . In most cases the keto form is more stable. 

    The reaction is very well termed as Aldol condensation . In case of ethanal this reaction , in the simplest form , can be represented as -

     

    2CH3 CHO  <------dil .NaOH ----------->   CH3 - CH (OH) -CH2 -  CHO------------- {tex}\Delta{/tex} /  ( - H2 O ) ------------->   CH2 - CH=CH - CHO. -

    Ethanal...................................................3- Hydroxybutanal.....................................................................But -2 - enal(

    ....................................................................( Aldol ).....................................................................( Aldol condensation product ) 

     

     

     

     

    Answered by Dr. Kamlapati Bhatt (Jun 30, 2017 8:58 p.m.)
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A delta is formed at the meting point of sea water and river water. Why? 

Posted by Mamta Bhati (Jun 29, 2017 9:25 p.m.) (Question ID: 6259)

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  • Sea water contains a lot of electrolytes. River contains colloids of sand and clay. When they meet the electrolytes neutralise the charge on colloidal particles and result in the precipitation of sand, clay etc. Thus resulting in a delta formation .

    Answered by Payal Singh (Jun 30, 2017 12:49 a.m.)
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Why adsorption always exothermic in nature. 

Posted by Mamta Bhati (Jun 29, 2017 9:23 p.m.) (Question ID: 6258)

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  • Adsorption is always exothermic. This statement can be explained in two ways.
    (i)Adsorption leads to a decrease in the residual forces on the surface of the adsorbent. This causes a decrease in the surface energy of the adsorbent. Therefore, adsorption is always exothermic.
    (ii)ΔH of adsorption is always negative. When a gas is adsorbed on a solid surface, its movement is restricted leading to a decrease in the entropy of the gas i.e., ΔS is negative. Now for a process to be spontaneous, ΔG should be negative.
    ΔG= ΔH-TΔS
    Since ΔS is negative, ΔH has to be negative to make ΔG negative. Hence, adsorption is always exothermic.

    Answered by Payal Singh (Jun 30, 2017 12:50 a.m.)
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Fluorine has a low electron gain enthalpy compared to chlorine, yet it is a 
more powerful oxidant. Explain why?

Posted by Sanjay Sharma (Jun 27, 2017 12:33 a.m.) (Question ID: 6200)

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  •  

    <pre>Main reason is the very high hydration enthalpy of the fluoride ion. That is because the ion is very small. There is a very strong attraction between the fluoride ions and water molecules. The stronger the attraction, the more heat is evolved when the hydrated ions are formed.</pre>

     

    Answered by Shweta Gulati (Jun 27, 2017 8:34 a.m.)
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Write the difference between osmosis and osmotic pressure?

Posted by Maria Chhakchhuak (Jun 25, 2017 5 p.m.) (Question ID: 6177)

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  • Osmosis is a phenomenon where in there happens to be  a movement of solvent particles ( ie. molecules  / ion )  from a solution  of lower concentration  to that of higher concentration when the two are separated from each other by a semipermeable membrane.

    while , 

    Osmotic pressure  is the pressure built up between the two solution undergoing osmosis . It is  caused due to a difference of vapour pressures  between  both the solutions. 

     

     

    Answered by Dr. Kamlapati Bhatt (Jun 25, 2017 8:09 p.m.)
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Can a solution have it's own osmotic pressure? Why. 

Posted by Amar Kumar Gupta (Jun 21, 2017 3:27 p.m.) (Question ID: 6081)

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  • No !  a solution of itself has vapour pressure , but not the osmotic pressure . Osmotic pressure comes into consideration only when the phenomenon of osmosis between two solutions with different vapour pressures   & separated by a semipermeable membrane    comes into play . 

    Answered by Dr. Kamlapati Bhatt (Jun 24, 2017 1:40 p.m.)
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Three atoms A, B and C crystallize in a cubic solid lattice where A atoms are present at the body centre, B atoms are present at the edge centre as well as at the corners of the cube and C atoms are present at the face centres of the cube. Now if all the atoms are removed from the two 4-fold axis and the one 2-fold axis passing through the cube, then the formula of the compound is?
Please its a bit urgent.

Posted by Swarup Rathi (Jun 21, 2017 11:27 a.m.) (Question ID: 6072)

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What do you mean by steric hindrance?

Posted by Sangharam Mohite (Jun 17, 2017 6:17 a.m.) (Question ID: 5968)

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  • Steric hindrance is the stopping of a chemical reaction which might be caused by a molecule's structure. An example of steric hindrance is how rotaxanes are created

    Answered by Payal Singh (Jun 17, 2017 7:12 a.m.)
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What do you mean by steric hindrance

Posted by Sangharam Mohite (Jun 17, 2017 6:17 a.m.) (Question ID: 5967)

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  • Steric hindrance is the stopping of a chemical reaction which might be caused by a molecule's structure. An example of steric hindrance is how rotaxanes are created

    Answered by Payal Singh (Jun 17, 2017 7:12 a.m.)
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Please tell me how can rate of dissolution of solid into water depends upon temperature not pressure?????

 

Posted by Saksham Phaugat (Jun 30, 2017 2:24 p.m.) (Question ID: 5903)

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  • When a solid solute is added  to the solvent like water , some solute dissolves  and its concentration increases in solution . This proces is known as as ' dissolution ' . Some solute particles in solution  collide with solid solute particles and get separated out of solution . This process is known as ' crystallisation '. A stage is reached when the ttwo processes occur at the same rate and thus a dynamic equilibrium is reached ,

    ..............................................Dissolution <----------->  crystallisation

    Factors affecting the rate of dissolution :

    (i)  Effect  of temperature -  

    The  rate of dissolution of a solid in a liquid is significantly affected  by temperature changes  as  the above dynamic equilibria must follow LeChatelier's Principle. In general , if the dissolution process is endothermic  ( {tex}\Delta H{/tex} sol < 0 ) , the solubility increases with rise in temperature. and if it is exothermic ( {tex}\Delta H{/tex} sol > 0 )   the rate of dissolution   decreases . These trends have been experimentally observed governing the concerned rate law too..

    (ii) Effect of pressure -

    Since both solids as well as liquids are highly incompressible , variations of pressure does not have any significant effect on tthe process or rate of dissolution of a solid in water.

     

     

     

     

     

     

    Answered by Dr. Kamlapati Bhatt (Jul 03, 2017 12:12 a.m.)
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Covalent solids are hard but maleable and ductile but GRAPHITE is also a covalent solid but is BRITTLE...i m confused plz help....

 

Posted by Mintu Rawat (Jun 09, 2017 1:42 p.m.) (Question ID: 5794)

  • Wrong question.

    First of all covalent compounds are neither maleble nor ductile. Covalent compounds like graphite, silicon carbide, quartz, diamond all are brittle i.e. breakdown on application of pressure.

    Posted by Harmanjit Singh (Jun 23, 2017 3:29 p.m.)
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  • Graphite is odd in its categorisation and does by no means rigorously follow the conventions of either a covalent solid, or a molecular solid (for example it can conduct electricity). Graphite has properties of both molecular solids (it is soft), and covalent solids (it has a very high melting point. In fact it will break down before it melts.).

    For this reason, the categorisation of some materials, such as graphite, can be somewhat complicated, and the idea of graphite being a covalent solid really just comes from its similarity with other covalent solids.

    Answered by Payal Singh (Jun 09, 2017 2:13 p.m.)
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What is dopent. 

How does dopent affect the conductivity of a semiconductor. 

 

Posted by Mamta Vaish (Jun 09, 2017 9:57 a.m.) (Question ID: 5783)

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  • Doping is nothing but adding N or P type impurities to a pure semiconductor. So these impurities will contain electrons or holes based on their impurity. When these kind of doping takes place in semiconductors and voltage is applied, these electrons will conduct electricity. In case of holes, electrons due to potential excitation jump from their original positions to these holes and form immobile ions at that point, whereas equal amount of holes are created from where these electrons jumped. Thus conductivity increases due to doping.

    Answered by Shweta Gulati (Jun 10, 2017 1:16 a.m.)
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